Apparatus for measuring phase difference

ABSTRACT

Apparatus for measuring phase differences of a rotating shaft by detecting a pair of generated AC frequencies adjacent the periphery of a tooth-wheel rotating at a fixed speed, even though the phase difference of the AC signals is greater or smaller that 2 pi .

United States Patent 9 [191 235/92PS, 92 CC; 324/83 D Maehara Aug. 21,1973 APPARATUS FOR MEASURING PHASE I DIFFERENCE [56] References Cited[75 I Inventor: Osamu Maehara, Kawasaki,Japan UNITED STATES PATENTS [73Assignee; Ona Sakki C0,, Ltd,,T0ky0,Japan 3,364,480 1/1968 Roth 340/347SY 3,549,870 12/1970 Lay.....' 235/92 PS [22] Filed: Oct. 26, 1971 [2]]Appl. No.: 192,200 Primary Examiner-Thomzis-A. Robinson AttorneySt0well& Stowell [30] Foreign Application Priority Data I Oct. 27, 1970 Japan45/93977 [57] ABSTRACT Apparatus for measuring phase differences of arotat- [52] US. Cl 340/347 SY, 340/207, 324/83 D, ing shaft by detectinga pair of generated AC frequen- 235/92 PS cies adjacent the periphery ofa tooth-wheel rotating at [51] Int. Cl. G01r 25/00, H03r 13/02 a fixedspeed, even though the phase difference of the Field of Search 340/347SY; AC signals is greater or smaller that 2 7r.

7 Claims, 5 Drawing Figures 7 "l6 1 PICKUP 0| FF. comm 001mm I,|| 2 3 I+9 l7 2| I DIFF.

FLlP- FLOP PICKUP DIFF] .coum

l l' 12' is I CONVERTER 19 20 FLIP-FLOP INVERTER CLOCK CLOCKPAfENTEnmczl ma 3.754.241

sum 1 o; 2

F1611 PRIOR ART FIG. 2

. PRIOR ART cm couumz PICKUP DIFF. l 8

IP- P PICKUP DIFF. FL 9 CLOCK FIG. 5

2n: 4n 6n:

This invention relates to apparatus for measuring electrical phasedifference, especially the phase difference of an electrical anglegreater than 2".

The invention will be more particularly described in reference to theaccompanying drawing wherein:

FIG. 1 illustrates an example of the principal structure of the knownapparatus for measuring a micro rotating angle;

FIG. 2 illustrates in block form an example of the circuit forprocessing signals detected by the said apparatus;

FIG. 3 illustrates in block form an example of preferred embodiments ofthe apparatus according to the invention;

FIG. 4 illustrates a wave form for explaining the theory of operation ofthe said apparatus according to the invention;

FIG. 5 illustrates a curve for explaining the theory of operation of thesaid apparatus according to the invention wherein the final indicationis made in the form of an analog signal. f

The apparatus for measuring a micro rotating angle is known in the artas shown, for example, in FIG. 1 of the drawings. I I

Referring now to the drawing in more detail, 1 is a ro tating disc madeof a magnetic material, the exterior circumference of which has beenprovided with toothed protuberances at a constant pitch. 2 is a drivingmotor for the said rotating disc. 3 is an electromagnetic pickupcomprising a detecting coil and a permanent magnet forming a magnet fluxwhich intersects thesaid detecting coil. The said electromagnetic pickup3 is situated facing the toothed proturberances on the exteriorcircumference of the said rotating disc 1 at a proper distance. 3' isanother electromagnetic pickup comprising a detecting coil and apermanent magnet like the said electromagnetic pickup 3. The saidelectromagnetic pickup 3' is fixed on a rotary shaft 5 facing thetoothed protuberances on the exterior circumference of the said rotatingdisc 1 at aproper distance. The said rotating shaft 5 hasthe same centeras that of a rotary shaft 4 for the said rotating disc 1, but can rotateindependently, and thereby the. said rotating disc 1 is allowed torevolvefreely withoutcontacting the said electromagnetic pickups 3 and3. The said electromagnetic pickup 3' can also revolve around the saidrotating disc 1 in accordance with the rotation of the said rotaty shaft5 within a range, where it does not come into contact with the saidelectromagnetic pickup 3.

A subject being measured is connected to the said rotary shaft 5. Thesubject is, for example, the supporting the magnetic flux from the saidelectromagnetic pickups 3 and 3" changes in accordance with the toothedprotuberances on the exterior circumference of the said rotating disc 1.Thus, the density of the magnetic flux intersecting the detecting coilbuilt in'each of the said electromagnetic pickups 3 and 3' is'caused tobar of an automatic weighing machine for measuring heavy materials. Itis known in the art of the automatic weighing machine that the bar is soconstructed that it begins rotating from the stateof response inaccordance with the difference in weight between the subject beingmeasured and the reference weight. Therefore, the said rotary shaft 5 isconnected to the bar of the automatic weighing machine so that theformer can rotate in accordance with the rotating angle of the latter.

Suppose the said rotating disc 1 is turned at a constant angularvelocity by the said driving motor 2, the

magnetic reluctance of the saidrotating disc 1 against change andthereby an AC signal having the same and constant frequency is derivedfrom each of these two pickups. There is a phase difference between theAC signals determined by the position having a mechanical and mutualrelationship between the said electromagnetic pickups 3 and 3'.

When rotating the said rotary shaft 5 in accordance with the angulardisplacement of a subject being measured, the said electromagneticpickup 3 revolves around the said rotating disc 1, causing the positionhaving a mechanical and mutual relationship between the saidelectromagnetic pickups 3 and 3' to change and thereby the phasedifference of the AC signal derived from each of these twoelectromagnetic pickups is caused to change. Therefore, the rotatingangle of the said rotaryshaft 5 can be determined or measured bydetecting the change of the phase difference. Also, the angulardisplacement of the subject being measured can be obtained from therotating angle of the said rotaryshaft 5 by detecting the change of thephase difference.

FIG. 2 is a block diagram showing an example of the known circuit fordetecting the change of the phase difference described in the precedingparagraph. In the drawing, 3 and 3' are electromagnetic pickupsillustrated and described in FIG. 1. 6 and 6' are differentiationcircuits. 7 is a flip-flop circuit. 8 is a gate circuit. 9 is a clockpulse generator. 10 is a counter.

Specifically, the AC signal outputs of the said electromagnetic pickups3 and 3' are differentiated individually by the said differentiationcircuits 6 and 6, and, for example, only positive differential pulsesignals of each signal thus differentiated are taken out and fed to thesaid flip-flop circuit 7. The actuation of the said gate circuit 8iscontrolled, in turn, by the output signals of the said flip-flopcircuit 7.

The said gate circuit 8is put into a conducting state I by the outputsignal ofthesaid flip-flop circuit 7, which matches, for example, thedifferential pulse signal derived ,from they said differentiationcircuit 6 and it is disabled by the output signal matching thedifferential pulse signal derived from the said differentiation circuit6'. The duration of the conductance of the said gate citcuit 8 becomesproportional to the phase difference of the AC signals taken out of thesaid electromagnetic pickups 3 and 3'. Therefore, the phase differenceof the output AC signals of the said electromagnetic pickups 3 and 3'can be obtained by computing the number of clock pulse signals, i.e.,pulse signals generated by the clock pulse generator, passing throughthe said gate circuit 8 when it is in aconducting state and applied tothe counter 10.

As described hereinbefore, when the change of the phase difference ofthe output AC signals of the said two electromagnetic pickups 3 and 3occurs as a result of the change in the position having a mechanicalandmutual relationship between these two electromagnetic magnetic pickups 3and 3', causing the duration of the conductance of the said gate circuit8 to change accordingly. Therefore, the change of phase difference canbe obtained by reading the indication of the said counter 10 at thattime. When detecting the phase difference using the circuit illustratedand described in FIG. 2, when, the rotating angle of the saidelectromagnetic pickup 3' becomes great particularly if the phasedifference of the output AC signals of the said electromagnetic pickups3 and 3 is greater than 2n, for instance, 211 0, the phase differencedetected is-not 2n 6 but 0. In other words, the detection is limited toa small rotating angle within a pitch of the toothed protuberances onthe exterior circumference of the said to tating disc 1 illustrated inFIG. 1.

It may be possible to expand the detective range of a rotating angle bycoarsing the pitch of the toothed protuberances on the exteriorcircumference of the said rotating disc 1. However, this is notpractical as the detecting accuracy deteriorates also.

It is accordingly an object of the invention to provide an improvedapparatus for measuring phase difference whereby the rotating angle ofthe said electromagnetic pickup 3' can be detected electrically even ifit rotates over the plural number of pitches of the toothedprotuberances on the exterior circumference of the said rotating disc 1illustrated in FIG. 1.

It is a further object of the invention, generally speaking, to providean apparatus for measuring phase differences capable of detecting thephase difference of the two AC signals even if it is smaller or greaterthan 211 radiens.

Electrically, the phase difference of the two AC signals are alwayshandled within a range less than 211'. For example, the phase differenceof 211' is handled as equal to the phase difference of 0. However, whenelectrically measuring a rotating angle over several pitches of thetoothed protuberances of the said rotating disc 1 with the angulardisplacement measuring apparatus as shown in FIG. 1, it is necessary todistinguish a phase difference of 211 6 from that of 0. Further, whendetecting the phase difference of 411' 0, it is needed to discriminateit from the phase difference of 0. It is, therefore, another object ofthe invention to provide an improved apparatus making it possible tocarry out such detection. l

The rotating angle detecting accuracy can be increased by providing therotatingdisc l illustrated in FIG. 1 with fine teeth or prptuberances onthe exterior circumference. Therefore, by using the apparatus accordingto theinvention with the apparatus as shown in FIG. 1, the detectingrange of a rotating angle can be expanded up to greater than 211' in amechanical angle while retaining high detecting accuracy.

A better understanding of this invention may be had from the followingdetailed description when read in connection with the accompanyingdrawings.

Referring now to FIG. 3 of the drawings, there is shown in block form anexample of preferred embodiments according to the invention, wherein:

11 and 11 are the sources of the generation of AC signals whichcorrespond, for example, to the said electromagnetic pickups 3 and 3';

l2 and 12 are differentiation circuits;

14 is a clock pulse generator;

1 is a phse inverting circuit;

16 and 16 are differentiation circuits;

17 is a reversible counter which, for example, utilizes pulse signalsfrom the said differentiation circuit 16 as add input signals and thosefrom the said differentiation circuit 16' as subtract input signalsrespectively;

18 is a clock pulse generator;

19 is a frequency converting circuit or rate multiplier;

20 is a counter; and

21 is a polarity discriminating circuit for the phase difference beingmeasured, comprising, for example, a reversible counter.

Suppose each output signal of the said AC signal generators 11 and 11'is a square wave signal having the same frequency as shown, for example,in FIG. 4(a) and 4(a) and having a certain phase difference. Each outputsignal is differentiated individually by the said differentiationcircuits 12 and 12 and, for example, only the positive pulse signals asshown in FIG. 4( b) and 4(b') are derived therefrom and fed to the saidflipflop circuits 13 and 13' respectively. Furthermore, either of thesaid flip-flop circuit 13 or 13, for example, the former is resetdirectly by applying to it the output pulse signal (as shown in FIG.4(c) of the said clock pulse generator'14.

On the other hand, the output. pulse signal of the said clock pulsegenerator 14 is supplied to the said flip-flop circuit 13 through thesaid phase inverting circuit 15 in order to reset it.

Thus, by setting and resetting the said flip-flop circuits l3 and 13individually, the output signal of the former is as shown in FIG. 4(d)and that of the latter is as illustrated in FIG. 4(d) respectively. Whendifferentiating these output signals individually with the saiddifferentiation circuits l6 and 16' and then deriving therefrom only thenegative pulse signals, such negative pulse signals as shown in FIG.4(e) and 4(e') can be obtained. When selecting the repetition period ofthe out-' put pulse signal (as shown in FIG. 4(c)) of the clock pulsegenerator 14 which is sufficiently shorter than the repetition period ofsignals being measured (as shown in FIGS. 4(a) and 4(a)), the phasedifference of the output negative pulse signals (as shown in FIGS. 4(e)and 4(e') of the said differentiation circuits l6 and 16' can be matchedwith that of the signals being measured (as shown in FIGS. 4(a) and 4(a)with practically sufficient accuracy.

As described hereinbefore, the said flip-flop circuit 13 directlyutilizes the output signals of the said clock pulse generator 14 as itsreset signal and the said flipflop circuit 13 uses the output signals ofthe said clock pulse generator 14 with their phase inverted as its resetsignal respectively. In other words, each reset signal of the saidflip-flop circuits 13 and 13' has an anti-phase relationship to eachother, and therefore the output negative pulse signals of the saiddifferentiation circuits 16 and 16 (FIGS. 4(e) and 4(e')) areasychronized completely with each other (i.e., they do not have the samephase when the phase difference is greater than 211-) and prevent thereversible counter 17 which will be described hereinafter from making anerratic operation.

Suppose the initial reading of the reversible counter 17 is n, thereading will be n+1 when the first pulse signal of the output signal(FIG. 4(e)) of the said differentiation circuit 16 is supplied to thecounter as an add input signal. When the first pulse signal of theoutput signals (FIG. 4(e')) of the said differentiation circuit 16' issupplied to the said counter 17 as a subtract input signal, the readingwill return to n. Likely, every time the output negative pulse signalsof the said'differentiation circuits l6 and 16' are alternately suppliedto the said reversible counter 17, the indication on the counter will ben+1 and n alternately. As shown in FIGS. 4(e) and 4(e), if delay of thephase of e against e, i.e., a phase difference, is kept small, the timeholding the indication of n on the said reversible counter will belonger than that of n+1. As the delay is increased close to 'n', thetime holding the indication of a n becomes shorter gradually, althoughit is still longer than the time holding the indication of n+1. If thephase difference between e and e is 11', the time holding the indicationof n will be equal to that of n+1. If the phase difference is greaterthan 1r, the time holding the indication of n+1 will be longer than thatof n.

FIGS. 4(f) and 4(f') illustrate the output negative pulse signals of thesaid differentiation circuits 16 and 16' with a phase difference betweenthe AC signals of 211' plus 0. When matching f2 pulse signal of the fpulse train to f'l pulse signal of the f' pulse train, the phasedifference between these two pulse trains will be 0 less than 211 Whenmatching f1 pulse signal of the f pulse train to j'l pulse signal of 1'pulse train, the phase difference between the two pulse trains will be211' 0.

The apparatus according to the invention is capable of detecting andmeasuring the phase difference greater than 21r. That is, when supplyingthe fi pulse signal of the f pulse train to the said reversible counter17, the initial indication on the counter will change from n to n+1.When the next f2 pulse signal of the f pulse train is supplied to thereversible counter 17, the indication will change from n+1 to n+2. Whena further f'l pulse signal of 1" pulse train is supplied to the counter,the indication will change to n+1. Thus, the reversible counter 17 willindicate n+2 and n+1 alternately and as the phase difference becomesgreater within a range from 211' to 411', the time holding theindication of n+2 will be longer. If the phase difference between thesetwo pulse trains is within a range from 41r to 611, the reversiblecounter 17 will indicate n+3 and 'n +2 alternately. The same indicationconsideration as above may be taken even if the phase difference isgreater than 6n.

If the phase difference of these two pulse trains is smaller than 211'as shown in FIGS. 4(e) and 4(e), and the phase of e-is delayed againstthat of e counter to phase relationship "illustrated in FIG. 4, thereversible counter 17 indicates n-1 and n alternately. Like f and 17 andthereby the repetition frequency of the output pulse signal of the saidclock pulse generator 18 is converted and in turn modified in accordancewith the output from counter 17. Therefore, the repetition frequency ofthe output pulse signal converted with the said frequency convertingcircuit 19 matches the computation of the reversible counter 17. Becauseof this, when supplying the converted pulse signal of the circuit 19 tothe counter 20 and allowing it to count for a predetermined period oftime, the computation will match the computation of the reversiblecounter 17 and its holding time, and thereby the phase difference can beobtained.

The phase difference can be indicated as an electrical angle byselecting properly the relationship between the computation of thecounter 20 and its indication. Also, the change in a mechanical anglecan be directly indicated when using the apparatus according to theinvention with the rotating angle detecting apparatus as shown in FIG.1.

Also, the polarity of the phase difference, i.e., the ad vance or delayof the phase, can be determined by the computation of the reversiblecounter 21 after supplying the counter with the carry forward andbackward signals from the reversible counter 17 as add and subtractinput signals. i

Mention has not been made of the number of bits of the reversiblecounters'l7 and 21 hereinbefore.

Referring now to it, suppose the number of bits of the reversiblecounter 17 is, for example, 1, the carry for ward (or backward) signalis transferred by the reversible counter 17 when the add input signal(or subtract input signal) to be provided continuously exceeds 1 bit jillustrated in FIG. 4, if f runs behind f' while the phase differencebetween these two pulse trains is within a range from 2 to 41r, thereversible counter 17 will indicate n-2 and n-l alternately. If thephase difference is further increased greater than that range within therange of 411' to 61:, the reversible counter will indicate n-3 and n-2alternately. Therefore, the phase difference can be obtained bydetecting the alternate computation of the reversible counter 17 andtheir respective indication holding time.

As shown in FIG. 3, the control signal matching the computation of thereversible counter 17 is, in the invention, applied to the saidfrequency converting circult (or thin-out circuit) 19 and the frequencyconversion factor (or thin-out factor) is changed in accordance with thecomputation of the reversible counter and thereby the reversible counter21 is actuated and thus the range of an angle being measured, i.e., 211- 0 or 4 1r 8, is indicated. If the number of bits of the reversiblecounter 17 is great, the measurement of an angle can be achieved withoutusing the reversible counter 21 as far as the computing input is withinthe range of the bits.

Described hereinbefore is the case in which a phase difference isdigitally detected and measured. In addition to the digital indication,the computationof the reversible counter 17 can be analogicallyindicated with, for example, a voltmeter after converting it into theequivalent analog. In such an analog indication as this, there is aproportional relationship between a phase difference d) and the averagetimeof the analog converted voltage E (the average over a great numberof cycles of the computation of the reversible counter '17 and theholding time of the computation in one cycle),

as shown in FIG. 5 (wherein, X axis is d: and Y axis is voltage E). 7

Referring to FIG. 3, the drawing illustrates a case in which the saidclock pulse generators l4 and 18 are installed separately. It can be soconstructed, however, that these clock pulse generators can be usedcommonly.

I claim: A

1. Apparatus for measuring electrical phase differences between two ACsignals of the same frequency wherein the phase difference between thesignals may be smaller or greater than 2 1r radians comprising:

first and second circuit means for phase matching the phase differencefrequencies and phase of the two AC signals and v for forming pulsesignals havinga repetition frequency corresponding to the frequency ofsaid AC signals,

first and second flip-flop means each having a set input and a resetinput,

means connecting the set input of said first flip-flop means to saidfirst circuit means for receiving the pulse signals from said firstcircuit means,

means connecting the set input of said second flipflop means to saidsecond circuit means for receiv ing said pulse signals from said secondcircuit means,

a first clock pulse generator having a first output electricallyconnected to the reset input of said first flip-flop means and a secondoutput electrically connected to the reset input of said secondflip-flop means to thereby reset said first and said second flip-flopmeans in response to the output pulses of said first clock pulsegenerator;

a first reversible counter having an add input and a subtract input, afirst output for providing either a carry forward signal or a carrybackward signal and a second output for providing a control signalcorresponding to the computation of said reversible counter, means forconnecting the output signals from one of said flip-flop means to theadd input and the output signals from the other of said flipflop meansto the subtract input,

a second clock pulse generator, I

frequency converting circuit having a first and a Second input, meansfor connecting the second output of said first reversible counterto-said first input and the output of said second clock pulse generatorto said second input, said frequency converting circuit being operableto change the repetition frequency of its output signal in accordancewith the computation of said first reversible counter and counterconnected to receive the output signals of said frequency convertingcircuit.

2. Apparatus as set forth in claim 1 further including a secondreversible counter connected to the first output of said firstreversible counter and operable to respond to the carry forward signalto perform an add computation and to the carry backward signal toperform a subtract operation.

3. Apparatus as set forth in claim 1 further including phase invertermeans having an input connected to receive the output of saidfirst-clock pulse generator and an output connected to the reset inputof said second flip-flop means.

4. Apparatus for measuring electrical phase differences between two ACsignals of the same frequency wherein the phase difference between thesignals may be smaller or greater than 2 7r radians comprising:

first and second circuit means for phase matching the frequencies andphase of the two AC signals and for forming pulse signals having arepetition frequency corresponding to the frequency of said AC signals,

first and second flip-flop means each having a set input and a resetinput, means for connecting the set input of said first flip-flop meansto receive said pulse signals from said first circuit means to therebyset said flip-flop circuit, means connecting the set input of saidsecond flip-flop means for receiving said pulse signals from said secondcircuit means to thereby set said second flip-flop means, a first clockpulse generator means having a first output for providing reset signalsto saidflip-flop circuits, means electrically connecting the reset inputof said first and said second flip-flop means to the output of saidfirst clock generator, a first reversible counter connected to receivethe output signals from one of said flip-flop means as an add inputsignal and the output signal from the other of said flip-flop means as asubtract signal and being operable in response to said add and subtractsignals to thereby perform an arithmetic computation and provide acontrol signal at one output and a carry forward or a carry backwardsignal at a second output, a second reversible counter connected to thesecond output and being operable to respond to the carry forward signalof said first reversible counter to perform an add operation and to thecarry backward signal of the reversible counter to perform a subtractoperation, means for converting the computation of said first reversiblecounter into the form of an analog signal and indicator means responsiveto said analog signal for providing an indication corresponding to theoutput of said converting circuit.

5. Apparatus for measuring electrical phase differences between two ACsignals of the same frequency comprising 7 first and second means fordeveloping pulse signals corresponding to the frequency and phase of twoAC signals being measured,

a first and a second flip-flop circuit, means for apply- 5 ingindividually to said flip-flop circuits the output pulse signals fromthe said first and second means for setting said first and said secondflip-flops, respectively, I

a clock pulse generator having outputs connected to said flip-flopcircuits for resetting said flip-flop'circuits,.

a first reversible counter, means for applying to said counter theoutput signals of the said first flip-flop circuits as an add inputsignal and the output-signals of said second flip-flop circuit as asubtract input signal, and means for developing the'time mean value ofthe state of said first. reversible counter. 1

, 6. Apparatus as set forth in claim 5 wherein said means for developingthe time mean value'includes a frequency converting circuit, means forapplying to said frequency converting circuit a clock signal and meansconnecting said frequency converting circuit to the output of said firstcounter such that the output pulse train from said frequency convertingcircuit is integrated over a period of time in comparison with therepetitive period of said AC signals.

7. Apparatus as set forth in claim 6 further including a secondreversible counter having its input connected to the output of saidfirst reversible counter such that the carry forward and carry backwardsignals of said first reversible counter are received as add input andsubtract input commands, respectively.

'0 l III IO!

1. Apparatus for measuring electrical phase differences between two ACsignals of the same frequency wherein the phase difference between thesignals may be smaller or greater than 2 pi radians comprising: firstand second circuit means for phase matching the frequencies and phase ofthe two AC signals and for forming pulse signals having a repetitionfrequency corresponding to the frequency of said AC signals, first andsecond flip-flop means each having a set input and a reset input, meansconnecting the set input of said first flip-flop means to said firstcircuit means for receiving the pulse signals from said first circuitmeans, means connecting the set input of said second flip-flop means tosaid second circuit means for receiving said pulse signals from saidsecond circuit means, a first clock pulse generator having a firstoutput electrically connected to the reset input of said first flip-flopmeans and a second output electrically connected to the reset input ofsaid second flip-flop means to thereby reset said first and said secondflip-flop means in response to the output pulses of said first clockpulse generator; a first reversible counter having an add input and asubtract input, a first output for providing either a carry forwardsignal or a carry backward signal and a second output for providing acontrol signal corresponding to the computation of said reversiblecounter, means for connecting the output signals from one of saidflip-flop means to the add input and the output signals from the otherof said flip-flop means to the subtract input, a second clock pulsegenerator, a frequency converting circuit having a first and a secondinput, means for connecting the second output of said first reversiblecounter to said first input and the output of said second clock pulsegenerator to said second input, said frequency converting circuit beingoperable to change the repetition frequency of its output signal inaccordance with the computation of said first reversible counter and acounter connected to receive the output signals of said frequencyconverting circuit.
 2. Apparatus as set forth in claim 1 furtherincluding a second reversible counter connected to the first output ofsaid first reversible counter and operable to respond to the carryforward signal to perform an add computation and to the carry backwardsignal to perform a subtract operation.
 3. Apparatus as set forth inclaim 1 further including phase inverter means having an input connectedto receive the output of said first clock pulse generator and an outputconnected to the reset input of said second flip-flop means. 4.Apparatus for measuring electrical phase differences between two ACsignals of the same frequency wherein the phase difference between thesignals may be smaller or greater than 2 pi radians comprising: firstand second circuit means for phase matching the frequencies and phase ofthe two AC signals and for forming pulse signals having a repetitionfrequency corresponding to the frequency of said AC signals, first andsecond flip-flop means each having a set input and a reset input, meansfor connecting the set input of said first flip-flop means to receivesaid pulse signals from said first circuit means to thereby set saidflip-flop circuit, means connecting the set input of said secondflip-flop means for receiving said pulse signals from said secondcircuit means to thereby set said second flip-flop means, a first clockpulse generator means having a first output for providing reset signalsto said flip-flop circuits, means electrically connecting the resetinput of said first and said second flip-flop means to the output ofsaid first clock generator, a first reversible counter connected toreceive the output signals from one of said flip-flop means as an addinput signal and the output signal from the other of said flip-flopmeans as a subtract signal and being operable in response to said addand subtract signals to thereby perform an arithmetic computation andprovide a control signal at one output and a carry forward or a carrybackward signal at a second output, a second reversible counterconnected to the second output and being operable to respond to thecarry forward signal of said first reversible counter to perform an addoperation and to the carry backward signal of the reversible counter toperform a subtract operation, means for converting the computation ofsaid first reversible counter into the form of an analog signal andindicator means responsive to said analog signal for providing anindication corresponding to the output of said converting circuit. 5.Apparatus for measuring electrical phase differences between two ACsignals of the same frequency comprising first and second means fordeveloping pulse signals corresponding to the frequency and phase of twoAC signals being measured, a first and a second flip-flop circuit, meansfor applying individually to said flip-flop circuits the output pulsesignals from the said first and second means for setting said first andsaid second flip-flops, respectively, a clock pulse generator havingoutputs connected to said flip-flop circuits for resetting saidflip-flop circuits, a first reversible counter, means for applying tosaid counter the output signals of the said first flip-flop circuits asan add input signal and the output signals of said second flip-flopcircuit as a subtract input signal, and means for developing the timemean value of the state of said first reversible counter.
 6. Apparatusas set forth in claim 5 wherein said means for developing the time meanvalue includes a frequency converting circuit, means for applying tosaid frequency converting circuit a clock signal and means connectingsaid frequency converting circuit to the output of said first countersuch that the output pulse train from said frequency converting circuitis integrated over a period of time in comparison with the repeTitiveperiod of said AC signals.
 7. Apparatus as set forth in claim 6 furtherincluding a second reversible counter having its input connected to theoutput of said first reversible counter such that the carry forward andcarry backward signals of said first reversible counter are received asadd input and subtract input commands, respectively.